At/in the back of your mind - Idioms by The Free Dictionary
at/in the back of your mind
at the back of your mind
COMMON If something is at the back of your mind, you are aware of it, though it is not the main thing you are thinking about. It was not until they had eaten that Brigadier Ryle raised the subject that had been at the back of his mind throughout the meal. Always, at the back of my mind, was the fear that the depression might overcome me again.
at the back of your mind not consciously or specifically thought of or remembered but still part of your general awareness.
at/in the ˌback of your ˈmind in your thoughts, but not your main interest or concern: I think your father knew at the back of his mind that he was being deceived.